[1] | 1 | <chapter name="Electroweak Processes"> |
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| 2 | |
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| 3 | <h2>Electroweak Processes</h2> |
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| 4 | |
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| 5 | This page contains processes involving Prompt-photon, <ei>gamma^*/Z^0</ei> |
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| 6 | and <ei>W^+-</ei> production, plus a few with <ei>t</ei>-channel boson |
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| 7 | exchange. |
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| 8 | |
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| 9 | <h3>Prompt photon processes</h3> |
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| 10 | |
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| 11 | This group collects the processes where one or two photons are |
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| 12 | produced by the hard process. Additional sources of photons |
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| 13 | include parton showers and hadron decays. A <ei>pT</ei> cut |
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| 14 | is required to stay away from the unphysical low-<ei>pT</ei> region. |
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| 15 | An eikonalized description, intended to be valid at all <ei>pT</ei>, |
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| 16 | is included as part of the multiparton-interactions framework. |
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| 17 | |
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| 18 | <flag name="PromptPhoton:all" default="off"> |
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| 19 | Common switch for the group of all prompt photon processes, |
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| 20 | as listed separately in the following. |
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| 21 | </flag> |
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| 22 | |
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| 23 | <flag name="PromptPhoton:qg2qgamma" default="off"> |
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| 24 | Scattering <ei>q g -> q gamma</ei>. |
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| 25 | Code 201. |
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| 26 | </flag> |
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| 27 | |
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| 28 | <flag name="PromptPhoton:qqbar2ggamma" default="off"> |
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| 29 | Scattering <ei>q qbar -> g gamma</ei>. |
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| 30 | Code 202. |
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| 31 | </flag> |
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| 32 | |
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| 33 | <flag name="PromptPhoton:gg2ggamma" default="off"> |
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| 34 | Scattering <ei>g g -> g gamma</ei>. |
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| 35 | <note>Note:</note> This is a box graph. The full quark-mass dependence |
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| 36 | in the loop leads to very complicated expressions. The current |
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| 37 | implementation is based on assuming five massless quarks (see below), |
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| 38 | and thus is questionable at small (<ei>pT < m_b</ei>) or large |
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| 39 | (<ei>pT > m_t</ei>) transverse momenta. |
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| 40 | Code 203. |
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| 41 | </flag> |
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| 42 | |
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| 43 | <flag name="PromptPhoton:ffbar2gammagamma" default="off"> |
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| 44 | Scattering <ei>q qbar -> gamma gamma</ei>. |
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| 45 | Code 204. |
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| 46 | </flag> |
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| 47 | |
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| 48 | <flag name="PromptPhoton:gg2gammagamma" default="off"> |
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| 49 | Scattering <ei>g g -> gamma gamma</ei>. |
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| 50 | <note>Note:</note> This is a box graph. The full quark-mass dependence |
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| 51 | in the loop leads to very complicated expressions. The current |
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| 52 | implementation is based on assuming five massless quarks (see below), |
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| 53 | and thus is questionable at small (<ei>pT < m_b</ei>) or large |
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| 54 | (<ei>pT > m_t</ei>) transverse momenta. |
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| 55 | Code 205. |
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| 56 | </flag> |
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| 57 | |
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| 58 | <modeopen name="PromptPhoton:nQuarkLoop" default="5" min="3" max="6"> |
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| 59 | Number of quark flavours included in the box graphs resposible for |
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| 60 | <ei>g g -> g gamma</ei> and <ei>g g-> gamma gamma</ei> processes. |
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| 61 | Owing to the complexity if the massive expressions, quarks are treated |
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| 62 | as massless. The default value should be applicable in the range of |
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| 63 | transverse momenta above the <ei>b</ei> mass but below the <ei>t</ei> one. |
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| 64 | </modeopen> |
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| 65 | |
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| 66 | <h3>Weak boson processes</h3> |
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| 67 | |
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| 68 | Under this heading we group processes involving the production |
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| 69 | of a single electroweak gauge boson, i.e. a <ei>gamma^*/Z^0</ei> |
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| 70 | or a <ei>W^+-</ei>, or a pair of them, or one of them in |
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| 71 | combination with a parton. Since the three sets are partly |
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| 72 | conflicting, each is associated with its own group flag. |
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| 73 | In addition, <ei>t</ei>-channel exchange of such a boson |
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| 74 | between two fermions form a separate group. |
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| 75 | |
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| 76 | <p/> |
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| 77 | There is one flag that can be used to influence the <ei>gamma^*/Z^0</ei> |
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| 78 | structure in all the processes below where it is produced, unless |
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| 79 | otherwise stated. |
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| 80 | <modepick name="WeakZ0:gmZmode" default="0" min="0" max="2"> |
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| 81 | Choice of full <ei>gamma^*/Z^0</ei> structure or not in relevant |
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| 82 | processes. |
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| 83 | <option value="0">full <ei>gamma^*/Z^0</ei> structure, |
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| 84 | with interference included.</option> |
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| 85 | <option value="1">only pure <ei>gamma^*</ei> contribution.</option> |
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| 86 | <option value="2">only pure <ei>Z^0</ei> contribution.</option> |
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| 87 | <note>Note</note>: irrespective of the option used, the particle produced |
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| 88 | will always be assigned code 23 for <ei>Z^0</ei>, and open decay channels |
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| 89 | is purely dictated by what is set for the <ei>Z^0</ei>. |
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| 90 | </modepick> |
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| 91 | |
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| 92 | <h4>Boson exchange</h4> |
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| 93 | |
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| 94 | The two processes in this subgroup is included as part of the |
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| 95 | multiparton-interactions framework. |
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| 96 | |
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| 97 | <flag name="WeakBosonExchange:all" default="off"> |
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| 98 | Common switch for the group of <ei>gamma^*/Z^0</ei> |
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| 99 | or <ei>W^+-</ei> exchange between two fermions. |
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| 100 | </flag> |
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| 101 | |
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| 102 | <flag name="WeakBosonExchange:ff2ff(t:gmZ)" default="off"> |
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| 103 | Scattering <ei>f f' -> f f'</ei> via </ei>gamma^*/Z^0</ei> |
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| 104 | <ei>t</ei>-channel exchange, with full interference |
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| 105 | between the <ei>gamma^*</ei> and <ei>Z^0</ei>. |
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| 106 | Code 211. |
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| 107 | </flag> |
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| 108 | |
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| 109 | <flag name="WeakBosonExchange:ff2ff(t:W)" default="off"> |
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| 110 | Scattering <ei>f_1 f_2 -> f_3 f_4</ei> via </ei>W^+-</ei> |
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| 111 | <ei>t</ei>-channel exchange. |
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| 112 | Code 212. |
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| 113 | </flag> |
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| 114 | |
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| 115 | <h4>Single boson</h4> |
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| 116 | |
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| 117 | <flag name="WeakSingleBoson:all" default="off"> |
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| 118 | Common switch for the group of a single <ei>gamma^*/Z^0</ei> |
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| 119 | or <ei>W^+-</ei> production. |
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| 120 | </flag> |
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| 121 | |
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| 122 | <flag name="WeakSingleBoson:ffbar2gmZ" default="off"> |
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| 123 | Scattering <ei>f fbar -> gamma^*/Z^0</ei>, with full interference |
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| 124 | between the <ei>gamma^*</ei> and <ei>Z^0</ei>. |
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| 125 | Code 221. |
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| 126 | </flag> |
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| 127 | |
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| 128 | <flag name="WeakSingleBoson:ffbar2W" default="off"> |
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| 129 | Scattering <ei>f fbar' -> W^+-</ei>. |
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| 130 | Code 222. |
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| 131 | </flag> |
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| 132 | |
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| 133 | <flag name="WeakSingleBoson:ffbar2ffbar(s:gm)" default="off"> |
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| 134 | Scattering <ei>f fbar -> gamma^* -> f' fbar'</ei>. Subset of |
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| 135 | process 221, but written as a <ei>2 -> 2</ei> process, so that |
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| 136 | <ei>pT</ei> can be used as ordering variable, e.g. in multiparton |
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| 137 | interactions. Hardcoded for the final state being either of the |
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| 138 | five quark flavours or three lepton ones. Not included in the |
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| 139 | <code>WeakSingleBoson:all</code> set, but included in the |
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| 140 | multiparton-interactions framework. |
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| 141 | Code 223. |
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| 142 | </flag> |
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| 143 | |
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| 144 | <h4>Boson pair</h4> |
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| 145 | |
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| 146 | Note that, in the decay of the two vector bosons produced by an |
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| 147 | <ei>f fbar -> V V</ei> process, the full four-fermion correlations |
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| 148 | from the leading-order <ei>f fbar -> V V -> 4f</ei> matrix elements |
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| 149 | are included <ref>Gun86</ref> (with some extensions by the authors). |
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| 150 | The matrix elements are provided in the double-resonant approach, i.e. |
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| 151 | excludes graph like <ei>f fbar -> V -> f fbar -> f fbar V -> 4f</ei>. |
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| 152 | |
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| 153 | <flag name="WeakDoubleBoson:all" default="off"> |
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| 154 | Common switch for the group of pair production of <ei>gamma^*/Z^0</ei> |
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| 155 | and <ei>W^+-</ei>. |
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| 156 | </flag> |
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| 157 | |
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| 158 | <flag name="WeakDoubleBoson:ffbar2gmZgmZ" default="off"> |
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| 159 | Scattering <ei>f fbar' -> gamma^*/Z^0 gamma^*/Z^0</ei>. |
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| 160 | Code 231. |
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| 161 | </flag> |
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| 162 | |
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| 163 | <flag name="WeakDoubleBoson:ffbar2ZW" default="off"> |
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| 164 | Scattering <ei>f fbar' -> Z^0 W^+-</ei>. Note that here the |
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| 165 | <ei>gamma^*</ei> contribution is not (currently) included. |
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| 166 | Code 232. |
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| 167 | </flag> |
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| 168 | |
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| 169 | <flag name="WeakDoubleBoson:ffbar2WW" default="off"> |
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| 170 | Scattering <ei>f fbar -> W^+ W^-</ei>. |
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| 171 | Code 233. |
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| 172 | </flag> |
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| 173 | |
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| 174 | <h4>Boson and parton</h4> |
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| 175 | |
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| 176 | <flag name="WeakBosonAndParton:all" default="off"> |
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| 177 | Common switch for the group of production of a single electroweak |
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| 178 | gauge boson, i.e. a <ei>gamma^*/Z^0</ei> or a <ei>W^+-</ei>, in |
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| 179 | association with a parton, i.e. a quark, gluon, photon or lepton. |
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| 180 | These processes give first-order corrections to the ones in the |
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| 181 | <code>WeakSingleBoson</code> class, and both sets cannot be used |
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| 182 | simultaneously without unphysical doublecounting. The current class |
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| 183 | should only be used to study the high-<ei>pT</ei> tail of the |
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| 184 | gauge-boson production processes (for LHC applications at least |
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| 185 | <ei>pT</ei> > 20 GeV), while the ones in <code>WeakSingleBoson</code> |
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| 186 | should be used for inclusive production. |
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| 187 | </flag> |
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| 188 | |
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| 189 | <flag name="WeakBosonAndParton:qqbar2gmZg" default="off"> |
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| 190 | Scattering <ei>q qbar -> gamma^*/Z^0 g</ei>. |
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| 191 | Code 241. |
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| 192 | </flag> |
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| 193 | |
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| 194 | <flag name="WeakBosonAndParton:qg2gmZq" default="off"> |
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| 195 | Scattering <ei>q g -> gamma^*/Z^0 q </ei>. |
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| 196 | Code 242. |
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| 197 | </flag> |
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| 198 | |
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| 199 | <flag name="WeakBosonAndParton:ffbar2gmZgm" default="off"> |
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| 200 | Scattering <ei>f fbar -> gamma^*/Z^0 gamma</ei>. |
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| 201 | Code 243. |
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| 202 | </flag> |
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| 203 | |
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| 204 | <flag name="WeakBosonAndParton:fgm2gmZf" default="off"> |
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| 205 | Scattering <ei>f gamma -> gamma^*/Z^0 f</ei>. |
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| 206 | Code 244. |
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| 207 | </flag> |
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| 208 | |
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| 209 | <flag name="WeakBosonAndParton:qqbar2Wg" default="off"> |
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| 210 | Scattering <ei>q qbar -> W^+- g</ei>. |
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| 211 | Code 251. |
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| 212 | </flag> |
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| 213 | |
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| 214 | <flag name="WeakBosonAndParton:qg2Wq" default="off"> |
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| 215 | Scattering <ei>q g -> W^+- q</ei>. |
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| 216 | Code 252. |
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| 217 | </flag> |
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| 218 | |
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| 219 | <flag name="WeakBosonAndParton:ffbar2Wgm" default="off"> |
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| 220 | Scattering <ei>f fbar -> W^+- gamma</ei>. |
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| 221 | Code 253. |
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| 222 | </flag> |
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| 223 | |
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| 224 | <flag name="WeakBosonAndParton:fgm2Wf" default="off"> |
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| 225 | Scattering <ei>f gamma -> W^+- f</ei>. |
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| 226 | Code 254. |
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| 227 | </flag> |
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| 228 | |
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| 229 | <h3> Photon Collision Processes</h3> |
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| 230 | |
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| 231 | A few electroweak two-photon production processes are available. |
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| 232 | To use them, photon PDFs have to be defined for the incoming |
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| 233 | beam particles. For proton beams an appropriate set would be |
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| 234 | MRST QED 2004 <ref>Mar05</ref>, available in the LHAPDF library. |
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| 235 | |
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| 236 | <flag name="PhotonCollision:all" default="off"> |
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| 237 | Common switch for the group of six processes presented below. |
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| 238 | </flag> |
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| 239 | |
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| 240 | <flag name="PhotonCollision:gmgm2qqbar" default="off"> |
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| 241 | Scatterings <ei>gamma gamma -> q qbar</ei>, where <ei>q</ei> |
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| 242 | is a light quark (<ei>u, d, s</ei>) . |
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| 243 | Code 261. |
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| 244 | </flag> |
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| 245 | |
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| 246 | <flag name="PhotonCollision:gmgm2ccbar" default="off"> |
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| 247 | Scattering <ei>gamma gamma -> c cbar</ei>. |
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| 248 | Code 262. |
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| 249 | </flag> |
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| 250 | |
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| 251 | <flag name="PhotonCollision:gmgm2bbbar" default="off"> |
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| 252 | Scattering <ei>gamma gamma -> b bbar</ei>. |
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| 253 | Code 263. |
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| 254 | </flag> |
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| 255 | |
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| 256 | <flag name="PhotonCollision:gmgm2ee" default="off"> |
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| 257 | Scattering <ei>gamma gamma -> e+ e-</ei>. |
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| 258 | Code 264. |
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| 259 | </flag> |
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| 260 | |
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| 261 | <flag name="PhotonCollision:gmgm2mumu" default="off"> |
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| 262 | Scattering <ei>gamma gamma -> mu+ mu-</ei>. |
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| 263 | Code 265. |
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| 264 | </flag> |
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| 265 | |
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| 266 | <flag name="PhotonCollision:gmgm2tautau" default="off"> |
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| 267 | Scattering <ei>gamma gamma -> tau+ tau-</ei>. |
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| 268 | Code 266. |
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| 269 | </flag> |
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| 270 | |
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| 271 | </chapter> |
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| 272 | |
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| 273 | <!-- Copyright (C) 2012 Torbjorn Sjostrand --> |
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| 274 | |
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